The walls of Jerusalem were breached by the Romans, in 69 CE, after a lengthy siege. (Three weeks later, after the Jews put up a valiant struggle, the Romans destroyed the second Holy Temple on the 9th of Av.)
The Jerusalem Talmud maintains that this is also the date when the Babylonians breached the walls of Jerusalem on their way to destroying the first Temple.

Practically speaking:

Healthy adults—bar- or bat-mitzvah age and older—abstain from eating or drinking between dawn and nightfall. Click here for exact times in your location.

Pregnant and nursing women may not have to fast. Someone who is ill should consult with a rabbi. Even those exempt from fasting, such as ill people or children, shouldn’t indulge in delicacies or sweets.A fast day is an auspicious day, a day when G‑d is accessible, waiting for us to repent

It is permitted to wake up early before the fast begins and eat, provided that prior to going to sleep one had in mind to do so.

During the morning prayers we recite selichot (penitential prayers), printed in the back of the prayerbook. The “long Avinu Malkeinu” is recited during the morning and afternoon prayers.

The Torah is read during the morning and afternoon prayers. The reading—the same for both morning and afternoon—is Exodus 32:11–14 and 34:1–10, which discusses the aftermath of the Golden Calf incident, how Moses successfully interceded on the Israelites’ behalf and attained forgiveness for their sin. After the afternoon Torah reading, the special fast-day haftarah, Isaiah 55:6–56:8, is read.

During the Amidah prayer of the afternoon service (Minchah), those who are fasting add the paragraph Aneinu in the Shema Koleinu blessing. (It is also added in the cantor’s repetition of the Amidah in both the morning and afternoon services, as its own blessing between the blessings of Re’eh and Refa’einu. Additionally, the priestly blessing is also added in the repetition of the Amidah in the afternoon service.

If the 17th of Tammuz falls on Shabbat, the fast is postponed until Sunday. Click here for more about this Shabbat.

Abstaining from food and drink is the external element of a fast day. On a deeper level, a fast day is an auspicious day, a day when G‑d is accessible, waiting for us to repent.

The sages explain: “Every generation for which the Temple is not rebuilt, it is as though the Temple was destroyed for that generation.” A fast day is not only a sad day, but an opportune day. It’s a day when we are empowered to fix the cause of that destruction, so that our long exile will be ended and we will find ourselves living in messianic times; may that be very soon.

Historians have long debated when this occurred: some maintain that Apostomos was a general during the Roman occupation of Israel, while others contend that he lived years earlier and was an officer during the Greek reign over the Holy Land.

I am sorry that you are ill. If you write your Hebrew full name and your mom's, I will keep you in my prayers.

Miriam

miriam

July 15, 2014

to Shira

Hi, please see this link for times in your location chabad.org/143790

Chabad.org Staff

July 15, 2014

When

When did it start in Cincinnati, Oh and when will it end?

ShiraCincinnati, Oh

July 15, 2014

Been so sick with Gastric problems and weight loss this year could barely fast on

Tish b'AV , Yom kippur , with too much coughing from bronchitis to need anything but water to stop disturbing the services. I am a Tevet 7 Birthday with a fast before and after my Birth date in Hebrew. Fasts were for when I was healthier and had family that observed, which they didn't , and a Jewish community by in large is not so pro active when I am sick or in crisis. I was moved out of walking distance of my observant neighborhood seven years ago, and still have no hope in sight to afford any return to an area where I can observe anything . Sorry HaShem

Joyce OxfeldPhiladelphia

July 15, 2014

It is wonderful to hear from you Mr Khan. I think the Moshiach must come first before the temple is rebuilt. The religion became more spiritual after the destruction of the Temple. To rebuild the temple first would be testing the Almighty. We do not test the Almighty, its the other way around. I agree that one has to do material and physical things as well like putting on Tephilin and giving to charity if one can afford to do so.

Philip LeamanLeeds

July 15, 2014

To Ellen

The fast began at 4:26AM in McGayheysville, VA and will end at 9:09PM. You can find fast times at this link

Chana Benjaminson

July 15, 2014

Washing on 17 Tammuz

Yes, you can wash yourself. The only prohibitions are eating and drinking.

On 9 Av and Yom Kippur, however, washing is prohibited.

MosheIsrael

July 15, 2014

to answer your question anon new yorker

If you want older sources try books such as the talmud, shulchan aruch, the arba'ah turim, or other jewish sources.

You can also find a rabbi and ask him.

moshe zalmannyc

July 14, 2014

Re: showering on fast days

Showering is permitted on fast days, with the exception of Tisha B'av and Yom Kippur.